Thermal isomerization of cyclobutenes. Part 17.—1-Ethyle-2-vinylcyclobutene and 1,2,3-trimethylcyclobutene

Abstract

The gas-phase thermal isomerizations of 1-ethyl-2-vinylcyclobutene and 1,2,3-trimethylcyclobutene have been studied in the temperature ranges 434–465 K and 424–464 K respectively. Both isomerizations are homogeneous and first order, and probably unimolecular. 1-Ethyl-2-vinylcyclobutene yields 2-ethyl-3- vinylbuta-1,3-diene, and the rate constants fit the Arrhenius equation, log k₁/s^–1= 13.729 ± 0.172–(149 390 ± 1 480 J mol^–1/2.303 RT). 1,2,3-Trimethylcyclobutene yields trans-2,3 dimethylpenta-1,3-diene as the only product and the rate constants fit the Arrhenius equation log k₂/s^–1= 13.276 ± 0.142–(141 180 ± 1 200 J mol^–1/2.303 RT). These results are consistent with noted insensitivity of the rates of isomerizations of cyclobutenes to the nature of the substituent, and are in line with the additivity relationships discussed previously.